Reversible air-water absorption heat pump

ABSTRACT

A cooling or heating device in an absorption heat pump of GAX type, including a generator, a GAX heat exchanger, an absorber, a condenser, an evaporator, a pump connected to the absorber and generator, and a first circuit for refrigerant solution circulating through the device and connecting together at least the generator, GAX heat exchanger, absorber, condenser, evaporator, and pump. A valve device modifies the first circuit to vary the manner in which the absorber, condenser, and evaporator are connected together. At least first and second heat exchanger units enable at least one phase of the circulating solution to be changed and to enable thermal energy to be exchanged against an external fluid, the first and second heat exchanger units each including at least two mutually separate sub-heat exchangers configured to function either as an evaporator or as an absorber and condenser, depending on an operating mode of the device.

The present invention relates to a cooling and/or heating device in anabsorption heat pump of GAX type, in accordance with thepre-characterising part of the main claim.

Devices of the aforesaid type are described for example in U.S. Pat. No.6,000,235, in U.S. Pat. No. 6,646,541 and in U.S. Pat. No. 4,719,767.The known devices comprise valve means for inverting the absorptioncycle at the evaporator and condenser, so that those heat exchangerswhich during operation in heating mode act as the condenser andevaporator are arranged to act respectively as the evaporator andcondenser during operation in cooling mode.

The devices of the aforedescribed type comprise at least two distinctand separate hydraulic circuits for dispersing the heat generated in theabsorber, and in the means which function as evaporator during operationin cooling mode and as condenser during operation in heating mode (seefor example U.S. Pat. No. 4,646,541). The presence of these two distincthydraulic circuits for dispersing the heat considerably complicates thecontrol and design both of the device overall and of the plant to whichthis device is connected.

Moreover in known devices the circuit through which the refrigerantsolution passes and which connects together the various components ofthe device requires relatively complicated and costly valve and controlmeans to ensure reliable passage of the device from one operating modeto the other; for example difficulties can arise because of the possibleaccumulation of solution and/or refrigerant within those circuitsections which are not in use, leading to uncertainties in the solutionand refrigerant level within the circuit, to cause operating instabilityand substantial variations in efficiency.

An object of the present invention is to provide an absorption coolingand/or heating device of GAX type which is more compact and of easieroperation and handling than traditional devices.

A further object is to provide a device which enables the hydraulicexchange circuit for the thermal energy generated or provided within theabsorber and in the evaporator/condenser to the simplified.

A further object is to provide a device which enables the valve andcontrol means present in the circuit for passage of the refrigerantsolution to be simplified.

These and further objects which will be apparent to an expert of the artare attained by a device in accordance with the characterising part ofthe accompanying claims.

The present invention will be better understood from the accompanyingdrawings which are provided by way of non-limiting example and in which:

FIGS. 1A, B are a schematic view of the device showing operation inheating mode and in cooling mode respectively;

FIGS. 2 and 3 are a simplified schematic view showing the connections ofthe various components of the device when operating in heating mode andin cooling mode respectively.

With reference to said figures, these show a usual generator 1, a heatexchanger 2 of GAX type, a usual pump 3, a usual subcooler-recuperator4, a usual rectifier 20 for the vapour prior to its entry into thecondenser and a usual vessel 21 for checking the refrigerantconcentration.

The said components and the relative connection circuit indicatedoverall by 7A-H are of conventional type and will therefore not bedescribed in detail hereinafter. The device also comprisessixteen/fourteen way valve means and two heat exchange means 9 and 10for changing a phase of the refrigerant solution circulating through thesaid means.

According to the invention, when the device operates in cooling mode(FIG. 3) the valve means 8 are arranged to modify the circuit whichconnects together the various components of the device such that thefirst heat exchange means 10 operates as an evaporator and the second 9operates partly as a condenser and partly as an absorber; in contrast,when the device operates in heating mode the evaporator means arearranged to modify said circuit such that the first heat exchange means10 operates partly as an evaporator and partly as an absorber, and thesecond 9 as an evaporator.

The heat exchange means 9 and 10 are of traditional type; preferably theheat exchange means 10 is of the fluid-liquid type and hence comprises ahydraulic circuit 11 (shown schematically in FIGS. 1A, 1B) to drive aliquid circulating through said circuit and passing through said heatexchanger. The hydraulic circuit will not be further described, being oftraditional type. Preferably the heat exchanger 10 is of the typedescribed in European application EP0911597, the description of which isto be considered as incorporated into the present text. The heatexchanger 10 comprises at least two tube bundles arranged to form twoseparate sub-heat exchangers 10A, B, C, presenting separate inlets andoutlets. In one possible implementation of the invention the separatesub-heat exchangers 10A, B, C are three in number and are disposed sideby side to form an “S”. It should be noted that for optimum operation ofthe heat exchanger 10, each of its parts 10A-C must comprise a tubebundle with tubes having a diameter between 8 mm and 16 mm. In thisrespect it has been verified experimentally that such heat exchangersenable the useful passage cross-sections for the fluids passing throughthem to be balanced in order to optimize the hydraulic characteristics(circuit pressure drops) and thermodynamic characteristics (heat andmass transfer and phase change) in both the modes in which the heatexchangers are required to operate. In known appliances in which thecycle inversion takes place only between evaporator and condenser therefrigerant flow rate is identical in both heat exchangers, and thephase change is in the opposite sense but with very similarthermodynamic characteristics; in contrast, in the present invention thecircuit inversion also involves the absorber, which has fluid flow ratesand thermodynamic characteristics completely different from theevaporator and condenser.

The heat exchange means 9 is of the fluid-air type and hence comprisesusual finning (not shown) for transferring to the surrounding air thethermal energy developed within the heat exchanger tubes. The heatexchanger 9 preferably comprises within a single bank two separatesub-heat exchangers 9A, B presenting separate connections indicated by12A, B and 13A, B, C acting, in the manner explained hereinafter, and atthe required time, as inlets or outlets for the solution circulatingthrough the device.

Advantageously the inlets 13A are split to optimize pressure drops andfluid balancing when operating in cooling mode.

It should be noted that the heat exchanger 9 is constructed as a singlebank for size and constructional reasons, but could be constructed astwo or more usual separate banks. In the same manner the heat exchanger9 could also be of fluid-liquid type even though such a solution wouldhave the complication of having to provide for each sub-heat exchanger ahydraulic circuit for circulating the liquid which is to receive or giveup the thermal energy developed or required during the phase changeswhich take place within said sub-heat exchangers.

From a functional schematic viewpoint the valve means 8 comprise twelveusual two or three-way valve members indicated by 14A-N, which can be ofany known type able to work with a refrigerant solution circulatingthrough a GAX device. These valve means could possibly be grouped into asingle multi-way device.

With reference to FIG. 2, the operating cycle of the device when inheating mode is such that the refrigerant vapour leaving the branch 7Gof the generator 1 via the valve 14B and the branch 15I reaches theinlet of the sub-heat exchanger 10A which in this operating modeoperates as a condenser. The vapour condenses within this condenser andbecomes liquid to generate heat which is transferred to the liquidcirculating through the heat exchanger and through the hydraulic circuit11 (FIG. 1A, B) connected to said condenser in order to be used forheating.

It should be noted that during this stage the valve 14C is also shiftedso that the dead branches 15E and F can also be reached by the vapour.

The relatively hot pressurized liquid passes through the outlet branch15E, the valve 14F, the branch 15C and the condensation valve 16 toreach the recuperator 4 in which, as described hereinafter, transfersheat to the vapour originating from the heat exchanger 9.

The refrigerant liquid then passes through the outlet branch 15D, theexpansion valve 17, the valves 14D and E and the inlet branches 15E, F,T, T, 13A, B and 12A, to enter either the whole of the heat exchanger 9or its part 9A or 9B. When in this operating mode this heat exchangeroperates as an evaporator to convert the entering liquid into vapour andto cool the air circulating over the heat exchanger, i.e. to recuperateheat from the outside.

It should be noted that during this stage the valves 14G, H are alsoshifted so that the dead branches 15E′ and 15T can also be reached bythe liquid.

The relatively cold, low pressure vapour from the outlet branches 12Aand 15V passes through the valves 14A, 14I and the branches 150, Q, Q′to the recuperator 4 where it receives heat from the liquid originatingfrom the condenser 10, and enters the heat exchanger 2 of GAX type viathe outlet branch 15R.

It should be noted that during this stage the valves 14G and 14L arealso shifted so that the dead branches 15P and 15O′ can also be reachedby the vapour.

From the GAX heat exchanger 2 the solution passes through the outletbranch 15S, the valves 14H and the branch 15E to enter the part 10B ofthe heat exchanger 10, and also passes through the outlet branch 15M,the valve 14N and the further branch 15H, H′ to also enter the otherpart 10C of the heat exchanger. When in this operating mode these twoheat exchanger parts 10B and 10C are in series and operate as anabsorber, to transfer heat to the liquid circulating through the saidheat exchangers 10B and 10C, which is used by the hydraulic circuit 11for heating.

The absorber could instead comprise a single sub-heat exchanger 10B or10C even though it has been found experimentally that two sub-heatexchangers positioned in series provide improved performance.

It should be noted that during this stage the valve 14M is also shiftedso that the solution can also reach the dead branches 15H, G.

The solution finally passes through the outlet branch 15N′, the valve14L and the branch 15U to reach the pump 3, from which it passes throughthe branch 15Z to reach the generator 1. It should be noted that duringthis stage the dead branches 15N′, N″ are also reached by the solution.

With reference to FIG. 3, the operating cycle of the device when incooling mode is such that the refrigerant vapour leaving the generatorthrough the branch 7G passes through the valve 14B to the inlet branch15A of the sub-heat exchanger 9A which in this operating mode operatesas a condenser. In this condenser the vapour is maintained underpressure and is cooled to become liquid. The vapour transfers heat tothe air surrounding the condenser 9A. The relatively hot pressurizedliquid leaves the condenser through the circuit branch 15B, and by wayof the valve 14F, a valve 16 and the branch 15C reaches the recuperator4 in which it transfers heat to the vapour originating from the otherheat exchanger 10 (as described in detail hereinafter). From therecuperator 14 the liquid passes through the branch 15D, the expansionvalve 17, the valves 14D, C and N, and the branches 15E-I, to reach thethree inlets of the three sub-heat exchangers 10A-C of the second heatexchanger 10 which when in this operating mode all operate asevaporator. The pressure of the liquid leaving the recuperator 4 islowered by the valve 17 and the liquid evaporates within the evaporator10 to absorb heat and thus cool the liquid circulating through theevaporator 10 and through the hydraulic circuit 11 (FIGS. 1A, B)associated with the evaporator, so as to produce the desired coolingeffect. The refrigerant vapour passes though the three outlets of theevaporator 10, the branches 15L-N, the valves 14G, N, L and the furtherbranches 15O-Q to reach the recuperator 4 where it is heated and fromwhich it enters the GAX heat exchanger 2 through the branch 15R. Theweak solution leaving the GAX heat exchanger passes through its outletbranch 15S, the valve 14H and the branches 15T to reach the secondsub-heat exchanger of the heat exchanger 9 which when in this operatingmode operates as an absorber. During the absorption process the heatgenerated is transferred to the air circulating about the heat exchanger9B. The solution leaving the absorber passes through the outlet branch15V, the valve 14I and the further branch 15U to reach the pump, andfrom there returns to the generator 1 via a branch 15Z.

It should be noted that by suitable shifting (represented in FIG. 3) ofthe valves 14A-N all the dead branches of the circuit are always incommunication with a branch in which the solution in one of its variousphases circulates.

FIGS. 1A, B show schematically the connections of the generator 1, ofthe GAX heat exchanger 2, of the recuperator 4, of the rectifier 20 andof the vessel 21. These connections have not been described in theaforegoing description and are not shown in FIGS. 2 and 3. As they areof conventional type for the expert of the art, they are not describedin detail hereinafter.

In FIGS. 1A and 1B the circuit flows which are common both to theheating stage and to the cooling stage are shown by full lines, thecircuit flows relative to the heating stage are indicated by dashed anddotted lines (FIG. 1A) and the circuit flows relative to the coolingstage are indicated by dashed lines (FIG. 1B).

When the device of the invention is in heating mode the heat exchanger 9can be defrosted. For this purpose, operation in heating mode isinterrupted and for a predetermined time, for example four minutes, thedevice is made to operate in cooling mode. In this manner a hightemperature solution is circulated through both parts 9A-B of the heatexchanger 9, to defrost the heat exchanger without the need to useexternal heat sources. This operation is also easier and quicker thanthat of the known art.

As the device of the invention comprises only two heat exchangers 9 and10 which, depending on the operating mode, perform the three functionsof evaporator, condenser and absorber, it is more compact and reliable.This arrangement also enables a single hydraulic circuit to be provided(FIGS. 1A, B) associated with the heat exchanger 10, for heating orcooling the liquid necessary to obtain the required operability of thedevice. In this manner the device is easier to handle and control andhas a smaller number of components than the devices of the known art.

It should also be emphasized that the device of the invention comprisesa hydraulic circuit with its valve members 14A-N controlled in such amanner that in no stage of its operation does it leave dead branches,i.e. branches not reached by the solution. Consequently, the circuit ofthe device requires a smaller number of overpressure members and ingeneral of control means, which are simpler and of easier handling.

Finally, it should be noted that the aforedescribed embodiment isprovided by way of example only, and that numerous variants arepossible, all entering within the same inventive concept; thus forexample the valve means 8 could consist of a plurality of differentvalve members instead of consisting of a single sixteen/fourteen-wayvalve.

1-15. (canceled)
 16. A cooling or heating device in an absorption heatpump of GAX type, comprising: a generator; a heat exchanger of GAX type;an absorber; a condenser; an evaporator; a pump connected to saidabsorber and generator; a first circuit for refrigerant solutioncirculating through the device and connecting together at least saidgenerator, GAX heat exchanger, absorber, condenser, evaporator, andpump; and a valve device configured to modify said first circuit to varya manner in which the absorber, condenser, and evaporator are connectedtogether; at least a first and a second heat exchange means for enablingat least one phase of the refrigerant solution circulating through saidfirst circuit to be changed and to enable thermal energy to be exchangedagainst an external fluid, said first and second heat exchange meanseach comprising at least first and second mutually separate sub-heatexchangers arranged to function either as an evaporator or as anabsorber and condenser, depending on an operating mode of the device.17. A device as claimed in claim 16, wherein when the device operates ina cooling mode, the valve device is configured to modify the firstcircuit such that the first heat exchange means operates as anevaporator, said first sub-heat exchanger of the second heat exchangemeans operates as a condenser and said second sub-heat exchanger of thesecond heat exchange means operates as an absorber, whereas when thedevice operates in a heating mode said valve device is configured tomodify said first circuit such that said first sub-heat exchanger of thefirst heat exchange means operates as a condenser and said secondsub-heat exchanger of the first heat exchange means operates as anabsorber, and the second heat exchange means operates as an evaporator.18. A device as claimed in claim 16, wherein the first and second heatexchange means comprise at least the first and second separate sub-heatexchangers that are only two in number.
 19. A device as claimed in claim16, further comprising a single hydraulic circuit for circulation of aliquid and configured to withdraw or receive thermal energy generated bythe evaporator or by the condenser or by the absorber.
 20. A device asclaimed 16, wherein the first circuit through which the refrigerantsolution circulates and the valve device are formed to avoid deadbranches not reached by said refrigerant solution, in two operatingmodes of the device.
 21. A device as claimed in claim 16, wherein in thesecond heat exchange means heat exchange takes place between therefrigerant solution and air circulating on an outside of said heatexchanger.
 22. A device as claimed in claim 16, wherein in the secondheat exchange means heat exchange takes place between the refrigerantsolution and a circulating liquid both of which lie within said secondheat exchange means.
 23. A device as claimed in claim 22, wherein thesecond heat exchange means comprises a substantially tube-shaped casinghaving an inlet and an outlet for a first fluid, and a plurality oftubes disposed longitudinally in an interior of said casing; each tubebeing connected to an entry element and an exit element for a secondfluid, the first fluid circulating within an interior of the casing incontact with outer solutions of said tubes; the tubes inside the casingbeing substantially directly in contact with each other and with theinner walls of said casing and having a cross-section to form within thecasing a plurality of micro-channels parallel to the tubes forcirculation of the first fluid.
 24. A device as claimed in claim 23,wherein between entry and exit portions the tubes present at least oneportion having a cross-section of shape different from that of adjacenttube portions, the shape being such as to at least partly break andremix the flow of fluid circulating through the tube, and portions ofthe tube having a cross-section of different shape being formed oftelescope shape and/or being in contact with each other, to maintain thetubes spaced apart.
 25. A device as claimed in claim 23, wherein theheat exchanger is of S shape, the casing housing the tubes comprisingtwo semi-circular shells in correspondence with a curved portion.
 26. Adevice as claimed in claim 22, wherein the second heat exchange meanscomprises three separate side-by-side sub-heat exchangers.
 27. A deviceas claimed in claim 16, wherein the valve device includes a single valvecomprising a plurality of valve members.
 28. A device as claimed inclaim 27, wherein the single valve is a sixteen/fourteen-way valve. 29.A method for controlling solution and/or refrigerant in a device claimedclaim 16, using the at least first and second separate sub-heatexchangers of the at least first and second heat exchange means eitheras an evaporator or as an absorber and condenser, according to theoperating mode of the device.
 30. A method for controlling solutionand/or refrigerant in a device claimed in claim 16, avoiding deadbranches not reached by said solution and/or refrigerant, in two modesof operation of the device.